1. Field of the Invention
The present invention relates to a process for selective fermentation.
2. Description of the Prior Art
When more than two substrates are to be metabolized by certain microorganisms, one that is readily-utilizable by the organism represses induction of the enzyme responsible for catabolism of the other substrate. This phenomenon is known as "Catabolite repression" [Hartwell, L. and B. Magasanik; J. Mol. Biol. 7, 401-420 (1963): Monod, J.; Recherches sur la croissance des cultures bacteriennes, thesis, Harman, Paris, 145 (1942)].
The above phenomenon is observed when microorganisms belonging to the Genus Pediococcus, such as Pediococcus halophilus, are cultivated in a medium containing more than two utilizable substrates as an energy source.
It has been known that catabolite repression as described above is observed in metabolism of not only substrates of energy sources for the microorganisms, including sugars, amino acids (e.g. arginine) and organic acids, but also in the metabolism of macromolecules such as nucleic acids, polysaccharides and proteins.
Thus, in general, there are many cases where some substrates are not utilized because of repression of the biosynthesis of their metabolic enzymes when readily-utilizable sugars, such as glucose and mannose, are present; or where desired enzymes are not produced.
Catabolite repression is one of the most powerful systems for metabolic regulation in Pediococcus, which becomes a problem in selective fermentation of the non-readily utilizable substrates as well as in production of certain enzymes or secondary metabolites. It has been almost impossible to release this repression. Only possible means are to cultivate for a very long period of time or to remove the substrate in the medium which is inhibitory to the selective fermentation. However, such fermentation requires additional cost or limits the use of natural medium which is cheap but has complicated composition.
Under the circumstances, the present inventors sought earnestly for efficient methods to release catabolite repression in microorganisms belonging to Pediococcus halophilus and found that phosphoenolpyruvate dependent sugar:phosphotransferase system (PTS) is present in these organisms and that catabolite repression can be released by inhibiting PTS.
PTS is the sugar transport system known in enteric bacteria, which was described by Kundig, W. et al. in Proc. Natl. Acad. Sci., U.S.A., 52, 1067-1074 (1964) and by P. W. Postma et al. in Microbiol. Rev., 49, 232-269 (1985). However, PTS has not been reported so far in Pediococcus.